The Divine Brush Horse Girl!

A former web-novel author transmigrates into the Uma Musume world as an untrained filly named Kazanatsu Shirayuki. Kazanatsu Shirayuki was just about to conquer the light novel newcomer awards, get an anime adaptation, and become the queen of entertainment... when she unexpectedly awakens a System. Once certain conditions are met, she can perfectly recreate scenes from her books. Kazanatsu Shirayuki decides to start writing Uma Musume fanfiction.

[In the debut race, Tokai Teio encounters the greatest rival of her life, gets utterly crushed, and loses. Furious, Teio returns to her dorm and secretly cries little tears.]

[Total popularity exceeds 10,000. Reward: One perfect recreation.]

Can she get stronger just by writing novels? ...When Tokai Teio sees the fanfiction, she thinks it's a joke. But she never expects that on the day of her debut, an unknown Uma Musume will suddenly rush out and kick her like a nobody on the roadside! As the book grows more and more popular, Orfevre and the Lady both meet the fates foretold in its pages! Years later, Kazanatsu Shirayuki stands at the pinnacle of the Uma Musume world. Everyone else finally discovers her writing secret identity and falls into deep thought: "So these were criminal threats?"

P.S. [The author used to be an Uma Musume, so this isn't made up.]

P.P.S. [Every word is typed by hand.]